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Up Topic Welding Industry / Metallurgy / welding joint
- - By mohamed radwan (*) Date 11-11-2010 12:03
dear all
i want to know what is the weakest point in the welded joint and what is the weakest area as well ?
thank you all
Parent - - By welderbrent (*****) Date 11-11-2010 14:54
Will depend upon the joint: lap, butt, corner, tee.  Will depend upon the weld: full penetration, partial, size of fillet, etc.  Will depend upon the quality of the weld and experience of the welder.  Will depend upon the welding procedures, if any, being followed.  Will depend upon the material being welded. 

There is much more information that would be required to TRULY ANSWER this question.  But there are many contributing factors that would alter the answer.

Have a Great Day,  Brent
Parent - - By mohamed radwan (*) Date 11-11-2010 23:09
i know what you mean sir, but you didn't understand my question , my question is in the geometry of the weld for example in a butt weld where is the weakest point that this point causes stress concentration and cracks may be applied by low stress , this question is related to the design of the weld not the process itself , as i was asked by an engineer and he asked me what is the weakest point in the welded joint not due to the process
Parent - - By Arctic 510 (**) Date 11-11-2010 23:19 Edited 11-11-2010 23:24
The toe of the weld is often the "weakest link" in a weld.  This is due mainly to geometry and subsequent stress concentrations.  The stress at the toe of a weld can be made greater or lesser through welding technique and proper application of acceptance standards (eliminating undercut, limiting reinforcement, etc.).  Cyclical (whether thermal or vibration) loads often result in cracks at the toes of weldements.  From my days in the mining industry to now in the petrochemical industry, the toe of a weld is by far where I have seen the most issues.  In a sound weld, however, the weld will have superior qualities compared to the base metal.
Parent - - By mohamed radwan (*) Date 11-12-2010 00:22
thx arctic ,
the toe of the weld , that what i thought too ,
but how about the HAZ should it be taken in consideration ?
Parent - By Lawrence (*****) Date 11-12-2010 00:38
Isn't the HAZ condition particularly dependent on Alloy and heat input <which is directly linked to process>  ?

I think you have been asked a bad question.. 

Or if it was a good question, you have not repeated it to us in it's complete form and context.
Parent - - By welderbrent (*****) Date 11-12-2010 14:10
And, not to repeat myself, the HAZ is directly affected by ALL the other factors previously mentioned. 

'THE WEAKEST PART'  is a very subjective question. 

And back to another part, if you have a partial joint penetration butt weld that then gets subjected to some form of torsion and the weld fractures right through the middle for the full length of the weld was it the toe that was the weakest link?  I have seen this plenty.  Yes, in log equipment and other heavy equipment one must be very careful of the profile especially at the toe and if there is not a smooth transition there it will often be the weak point at which a crack initiates.  But not always.  You can also gusset too strongly and then the stresses will find another weak point to start a failure.  Then, beyong the profile, the HAZ which comes back to proper procedures, process, joint geometry, etc. 

Based upon the original post and even the follow up I see no way to give you a one part answer to your question.  You have not supplied nearly enough information and as a general question there is no one right answer. 

Have a Great Day,  Brent
Parent - - By mohamed radwan (*) Date 11-13-2010 07:27
thank you brent that was helpful
Parent - - By 803056 (*****) Date 11-13-2010 21:10 Edited 11-13-2010 21:14
I have to agree that there is no one correct answer unless more details are provided.

In general, I would have to say the weak link in any joint would have to be associated with the critical discontinuity. The critical discontinuity would differ from one circumstance to another.

A change in geometry could be the critical discontinuity if the nature of the load is cyclic.

A stress riser such as a crack, rough surface, direction of the grinding marks, undercut, etc. could be the critical discontinuity if the nature of the load is cyclic or static depending on the orientation of the stress riser relative to the direction of the load.

In the case of heat treatable aluminum alloy the HAZ could represent the critical metallurgical discontinuity when the ultimate tensile strength of the HAZ is lower than either the weld or the adjacent base metal.

In the case of through thickness loading, oxides along the grain boundaries that enable lamellar tearing could be the trigger that initiates failure.

A poor design can result in weld failures even when the welds are "perfect." Residual stresses accumulate when you have multiple perpendicular welds intersecting at a common point. The sum of the vector components can exceed the ultimate tensile strength of the weld and result in the initiation of a crack.

This list could go on and on, but I believe there are enough examples listed to provide a basis for saying there is no single condition that would be the weak link in all cases.

I would categorize this as a brainteaser. Something to ponder. An excellent subject to discuss over a hot chocolate!

Best regards - Al
Parent - - By welderbrent (*****) Date 11-14-2010 15:46
Are you springing for the chocolate? 

Have a Great Day,  Brent
Parent - By 803056 (*****) Date 11-15-2010 05:18
Any time my friend.

- - By weldktm Date 07-03-2013 15:02
at this link you could see a good example for a susceptible welding point:
Parent - By jwright650 (*****) Date 07-03-2013 15:25
This is an example of lamellar tearing in the base metal, it's not specifically addressing the Op's question of the weakest part of the weld. I think the Op is asking about several areas mentioned earlier(toe of the weld, or the HAZ).
Up Topic Welding Industry / Metallurgy / welding joint

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